Sheet metal is rolled and formed into thin flat sheets or strips to be cut or formed into selected sized and shaped pieces. One of the fundamental types of material forms used in metalworking, sheet metal can be cut and bent into a variety of different shapes. Countless everyday objects are made of the material. Thicknesses can vary significantly, although extremely thin thicknesses are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate. Sheet metal thickness is denoted by gauge, sometimes spelled gage, which indicates a standard thickness before processing. Processing may include polishing or the applying of protective plastics which will decrease or increase a sheets thickness. As the gauge number increases the material's thickness decreases. Galvanized steel is thicker than regular steel because the process of galvanizing bonds a layer of zinc to the steel. The layer's thickness can be controlled. The thicknesses are based off of how many ounces per square foot of the galvanizing material is added to the base steel. For instance, some common gages of sheet metal are as follows:
SteelAluminumGalvanized SteelGageInches(mm)Inches(mm)Inches(mm)3.23916.073.22945.8274.22425.695.20435.1895.20925.314.19194.6206.19434.935.18194.1157.17934.554.16204.1158.16444.176.12853.2644.2709.14953.797.11442.906.15323.89110.13453.416.10192.588.13823.51011.11963.038.09072.304.12333.13212.10462.657.08082.052.10842.75313.08972.278.07201.829.09342.372141.897.083.06411.628.07851.99415.06731.709.05711.4500.7101.80316.05981.519.05081.290.06351.61317.05381.367.04531.151.05751.46118.04781.214.04031.024.05161.31119.04181.062.0359.912.04561.15820.0359.912.035.0320.03961.00621.0329.836.032.0285.0366.93022.0299.759.0253.643.0306.85623.0269.683.0226.574.0276.77724.0239.607.0201.511.0247.70125.0209.531.0179.455.0217.62726.0179.455.0159.404.0202.55127.0164.417.0142.361.0187.51328.0149.378.0126.320.0172.47529.0135.343.0113.287.0157.43730.0120.305.0100.254.0142.39931.0105.267.0089.226.0134.36132.0097.246.0080.203.34033.0090.229.0071.18034.0082.208.0063.16035.0075.191.0056.14036.0067.170.0050.127
One common use of sheet metal is the forming of air handling duct work which is used in most commercial and residential buildings and houses. Some of the duct work is prefabricated and delivered to the construction site. However, it is commonly necessary to fabricate at least some parts of the needed duct work on site. Installation workers on a job site are supplied with flat pieces of sheet metal and are required to cut and bend these pieces to the proper shape and size to be joined with other parts of the air handling structure. A tool which is used to help make straight and accurately placed bends in a piece of sheet metal is known as a ‘metal brake’ or simply a ‘brake’. A conventional brake typically has two jaws with adjacent straight edges which can be urged together to grasp a piece of sheet metal at a selected position whereupon, a third jaw is caused to swing down against a free portion of the metal piece near the edge of the first two jaws and bend the piece of metal to a desired angle. Brakes of this type are often large enough to bend a piece of sheet metal which is up to ten feet long. Therefore, this type of brake is either self standing with integral legs or is mounted on a worktable or bench and is large, heavy and cumbersome to move from one construction site to another.
A cross break is a term used to describe a piece of sheet metal subjected to multiple obtuse bend angles of a selected angle, for example, approximately 170° are made across a flat section of thin metal. Cross breaks formed in square or rectangular sheets are most commonly formed in an X pattern or shape wherein formation of the cross bends or creases create a central bulge defining a slight pyramid shape in the metal without overly distorting it. The crossing ridges forming the cross break stiffens the face of the metal and help prevent is from flexing and buckling under a load which would result in vibration or rattling of an end sheet without a cross break when the heating or cooling fan used in a HVAC system would start or stop. When used correctly this bending method offers a very cost effective way of strengthening your parts. Cross breaks are often incorporated on machine enclosures and duct work where the added rigidity reduces noise from vibration or air flow.
The main advantage of the cross break used to strengthen duct work is that it allows designers to use thinner gauges, thus saving money, and providing a more workable material for fabrication of custom vent components without compromising the strength of the part. Cross breaks do not need to be an X shape to strengthen a part and the brake of the instant invention can be used to create diagonal shapes, triangular shapes or straight angled edges such as flanges as well. Because the cross break can be used in applications where it is difficult to utilize a separate brace it can be used in place of light bracing for a variety of applications. The invention provides a single portable hand held braking tool to form cross breaks formed along bent faces and in single lines to stiffen shaped duct work in order that duct work requiring a custom sheet metal part can be fabricated on site, instantly.
It can be difficult to properly form a cross break with conventional metal bending tools because the bend extends diagonal to the straight edge of the part. For this reason, the bend lines are marked on the metal to be treated either by scoring or simply marking it with a marker or pencil. The sheet of metal is placed in the groove or gap between the spaced apart longitudinal brake members or bars and the break line aligned with the brake edge of the brake. The brake bars are squeezed together to firmly hold the metal therebetween and one hand is used to bend the sheet of metal slightly forming a shallow bend at an obtuse angle along the edge of the bar. The sheet is removed and rotated and placed back between the bars which is a slightly tighter fit in view of placement and alignment of the sheet having a diagonal bend therein between the longitudinal brake members at a selected angle. The braking process is repeated to form a cross break in the metal sheet.